Three phase, pole-changing rotary electric machine



THREE PHASE, POLE-CHANGING ROTARY ELECTRIC MACHINE Filed A ril 11, 1962March 23, 1965 s. H. RAwcuFFE 3 Sheets-Sheet 2 INVENTOR An -2 W ATTDRNE) March 23, 1965 a. H. RAWCLIFFE 3,175,143

THREE PHASE, POLE-CHANGING ROTARY ELECTRIC MACHINE Filed April 11, 19623 Sheets-Sheet 3 INVENTOR QM, QwfKWM ATTORNEY United States Patent 03,175,143 TIHQEE PHASE, POLE-CHANGING ROTARY ELECTRIC MACHINE GordonHindle Rawclifie, Clifton, Bristol, England, as-

signor to National Research Development Corporation, London, EnglandFiled Apr. 11, 1962, Ser. No. 186,700 Claims priority, application GreatBritain, Apr. 20, 1961, 14,243/ 61 6 Claims. (Cl. 318-224) Thisinvention relates to rotary electric machines, particularly tothree-phase, alternating current pole-changing electric motors adaptedto run at two alternative speeds.

It is well known to provide pole-changing A.C. electric motors havingeither separate sets of phase windings providing alternativepole-numbers or having a single set of phase-windings, with suitableconnections to the coils brought out to a multiple switch, so that thesingle set of phase-windings can be switched to provide alternativepole-numbers. The most common arrangements provide alternativepole-numbers in the ratio 2:1, and hence alternative operating speeds inthe reverse ratio.

Recently, a new principle for providing alternative pole-numbers in arotary electric machine with a single set of phase-windings has beendeveloped. This principle is known as Pole-Amplitude Modulation and hasbeen described in two papers by Professor G. H. Rawcliife and others,the earlier entitled Induction Motor Speed-Changing by Pole-AmplitudeModulation in the Proceedings of the Institution of ElectricalEngineers, vol. 105, Part A, No. 22, August 1958, and the later antitled Speed-Changing induction Motors-Further Developments inPole-Amplitude Modulation in the Proceedings of the Institution ofElectrical Engineers, vol. 107, Part A, No. 36, December 1960.

While the above-mentioned references give a full explanation of thegeneral theory of pole-amplitude modulation, it may briefly be said herethat a 3-phase, A.C. machine having a single set of three phase-windingswound to provide a first pole-number may be adapted to operate at analternative pole-number, in a ratio less than 2:1, if a pole-amplitudemodulation Wave, that is to say a cyclical pattern of reconnection ofthe coils, is applied to each phase-winding, the three modulating Wavesbeing relatively spaced by 120 around the axis of the machine.

The pole-amplitude modulation of each phase-winding is eiiected byswitching successive portions of the phasewinding around the peripheryof the machine so that, in the modulated connection, one portion isreversed in polarity and one portion retains its original polarity foreach complete cycle of the modulating wave.

A rotary electric machine according to the prior art referred to may bedefined as a rotary electric machine having a three-phase windingproviding a first pole-number of P pole-pairs and an alternativepole-number of either (P-i-M) or (PM) pole-pairs, having threephasewindings sequentially arranged around an axis, the electricalphase-sequence A, B, C and phase-band sequence +A C +B -A +C -B defininga reference sense of rotation around said axis, said phasebandscomprising coils connected together in each phase-winding to provide 2 Ppoles, means for connecting selected ones of said coils in analternative manner to modulate the relative amplitudes of said 2 P polesaccording to three-pole-amplitude modulation Waves applied one to eachphase-winding in spaced relationship, each pole-amplitude modulationwave comprising M cycles of alternate positive and negative partsfollowing sequentially from an origin, said positive and negative partsbeing identified by reversal of polarity of the poles of said negativepart relative to the poles of said positive part, the spacedrelationship of said poleamplitude modulation waves being such as tospace the origins thereof at three points spaced apart substantiallyone-third of a revolution around said axis, the sequence of saidpole-amplitude modulation waves at said three spaced points being in thephase sequence A, B, C or in the phase sequence A, C, B in the saidreference sense of rotation, as said alternative pole-number is (P-l-M)pole-pairs or (P-M) pole-pairs, respectively.

In addition, further expedients are known to ensure that the amplitudesof the poles, in the modulated connections, are not uniform but followmore nearly a sinusoidal amplitude distribution in each modulating wave.T 0 this end, one pole may be omitted at one end of each modulationhalf-cycle, or both end poles may be reduced in amplitude or the machinemay be Wound originally as a fractional-slot machine to provide asinusoidal distribution of the pole amplitudes for both the modulatedand unmodulated connections.

For alternative pole-number combinations where neither the unmodulatedpole-number for which the machine is wound nor the modulated pole numberobtained by poleamplitude modulation is a multiple of three poles,exactly the same pattern of reconnection of the coils may be used foreach of the three phase-windings. Such a system is known as symmetricalpole-amplitude modulation, because the distribution of coils, in boththe unmodulatcd and modulated connections, is always symmetrical aboutthe mid point of each half phase-winding.

Where either pole-number is a multitude of three, a more elaboratearrangement is required for two of the three phase windings. Such asystem is known as asymmetrical pole-amplitude modulation because, inthe modulated connection the distribution of coils is not symmetricalabout the mid points of each half of these two phasewindings.

The present invention, however, relates to machines using symmetricalpole-amplitude modulation, that is where neither pole-number is threepole-pairs or a multiple thereof.

Many of the known arrangements for symmetrical pole-amplitude modulationrequired the omission of coils in the modulated connection. Inparticular, machines Wound with an integral number of slots per pole forthe unmodulated pole number required the omission of coils to providethe sinusoidal amplitude distribution of the poles, in each modulationhalf-wave, in the modulated connection.

The coils removed from circuit on modulation have had to be Wound withhalf the number of turns, of double-section wire, compared with theremainder of the coils. This, though not a serious difficulty, can beobjectionable on either of two grounds:

(a) In small mass-produced machines, it involves extra care inmanufacture, to make certain that these special coils are inserted inthe proper slots. The connections are also a little more complicated tomake.

(b) For large machines, especially at low voltages, the number ofconductors is small, and may be an odd number. If this requires a smallodd number of turns per coil, it is clearly impossible to wind specialcoils with half the number of turns.

The object of the present invention is to provide an improvedpole-amplitude modulation arrangement, for a uniformly-distributedintegral slot machine, enabling all coils to be connected in circuit forboth the unmodulated and modulated connections.

Accordingly the present invention provides a rotary electric machinehaving a three-phase winding providing a first pole-number of Ppole-pairs and an alternative pole-number of either (P+M) or (P-M)pole-pairs, having three phase-windings sequentially arranged around anaxis, the electrical phase-sequence A, B, C and phaseband sequence +A C+B A +C B defining a reference sense of rotation around said axis, saidphasebands comprising coils connected together in each phasewinding toprovide 2P poles, means for connecting selected ones of said coils in analternative manner to modulate the relative amplitudes of said 2P polesaccording to three pole-amplitude modulation waves applied one to eachphase-winding in spaced relationship, each pole-amplitude modulationwave comprising M cycles of alternate positive and negative partsfollowing sequentially from an origin, said positive and negative partsbeing identified by reversal of polarity of the said poles of saidnegative part relative to the poles of said positive part, the spacedrelationship of said pole-amplitude modulation waves being such as tospace the origins thereof at three points spaced apart substantiallyonethird of a revolution around said axis, the sequence of saidpole-amplitude modulation waves at said three spaced points being in thephase sequence A, B, C or in the phase sequence A, C, B in the saidreference sense of rotation, as said alternative pole-number is (P-I-M)pole-pairs or (P-M) pole-pairs, respectively, wherein neither said firstpole-number nor said alternative polenumber is three pole-pairs or amultiple thereof, wherein the said three-phase winding is anintegral-slot Winding and wherein the pole-amplitude of a pole at oneend of each half of each phase-winding or the poles at both ends of eachhalf of each phase-winding is reduced in the alternative, that is to saymodulated, connection, said pole-amplitude reduction being effected byreversal in current-carrying sense of selected coils relatively to allthe remaining coils of the coil-groups providing said poles of reducedamplitude, whereby all coils of all phasebands are included in circuitfor both the first and the alternative connections.

From the preceding paragraph, it will be readily under stood that, inthe modulated connection, when a sinusoidal distribution ofpole-amplitudes in each modulation half-wave is desired, correspondingto the omission of one pole at one end of each half-wave or, preferably,the reduction of pole-amplitude at both ends of each half-wave, thedesired distribution is obtained by connecting coils of the samecoil-group concerned in opposition to each other, in current-carryingsense, so that the resultant pole-amplitude is reduced thereby.

Suppose for example, that according to earlier techniques it was desiredto remove from circuit two adjacent coils, in the same coil-group.Substantiall the same effect is obtained in a machine according to thepresent invention by leaving both coils in circuit and reversing onecoil with respect to the other. Since the two coils are adjacent, theyalmost exactly'neutralise each other when one is reversed, though thereis a very small vector diiference between the of the two coils. There isalso a very small high-harmonic component added .to the wave at thatpoint. Which of two coils it is the better to reverse, and which toleave connected in the original sense, can be determined by examinationof the vector diagram or of the equations for the whole winding.

In general, it is found that the choice of the coil for reversal shouldbe so made that, as nearly as possible, a regular and symmetricalmodulating wave is obtained for the winding as a whole.

When it is desired to make two coils mutually neutralising, and thesetwo coils .form part of a larger group of coils, that coil which liesnext to the rest of the coil-group should be connected in the same senseas the rest of the group. The other coil of the pair should be reversed.

Apart from the simplification in manufacturing specifications which anarrangement according to this invention makes possible, one verysubstantial design advantage arises tin regard to the ratio between thefluxdensities for the unmodulated and modulated polenumbers. Thevariation in the performance of a particular design, for a givenflux-density, between that when coils are omitted from circuit and thatwhen coils are arranged for mutual neutralisation, is very slight. It isin relation to obtaining full flux-density for both speeds thatdiliiculty sometimes arises, which can be resolved by the techniqueaccording to this invention.

The usual switching connections for machines using pole-amplitudemodulation are parallel-star/series-delta (or series-star). Thisarrangement requires six terminals. However, it is not possible with the6-terminal arrangement to exclude coils from circuit in the parallelstarconnection. This has necessitated the use of parallel-star for theunmodulated connection, and series delta (or series-star) for themodulated connection, for any modulation scheme which involves theexclusion of some coils on modulation.

For the same winding factor, parallel-star connections give a higherflux per pole than series-delta; and if the winding factor is reduced,the flux per pole is increased still further. This makes it advantageousto use parallelstar connections for the smaller pole-number; since theincrease in flux per pole is acceptable when the number of poles isreduced in proportion. The higher polenumber is then provided by eitherseries-delta or seriesstar connection.

However, it is usually preferred to reduce the polenumber by modulation,so that the parallel-star connection is particularly advantageous forthe modulated pole-numher. In this event, the unmodulated, higherpole-number is provided preferably by series-delta connection.

Avoidance of coil-omission on modulation is therefore a considerableadvance, especially when it is used to provide modulation to reducepole-number, with series-delta/ parallel-star connections.

In order that the invention may be readily carried into effect, oneembodiment will now be described in detail, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a slot-winding diagram for the three phasewindings of a3-phase machine showing at (a) a known arrangement for pole-amplitudemodulation of an 8-pole/ lO-pole Ii-phase winding on a 72-slot frame andat (b) the corresponding pole-amplitude modulation arrangement accordingto the present invention;

FIG. 2 is a full slot-winding diagram of one phase- Winding of themachine represented in FIG. 1(1)); and

FIGS. 3(a) and 3(b) show, respectively, the paralle star, 8-pole,unmodulated connection and the series-star, l0-pole, modulatedconnection of the machine of FIG. 1(b) and FIG. 2.

FIG. 1 shows the coil winding arrangement of a uniformly-distributedintegral-slot machine providing 8 poles on a 72-slot frame with threecoils per coil-group in the unmodulated connection.

The modulated connection of FIG. 1(a) is obtained by the reversal ofwhole coil-groups in the middle of consecutive half-waves of themodulation cycle, together with the reduction of end-poles of bothhalf-waves by coil omission, according to the notation:

00+1, +3, +3, +100, 00-1, +3, +3, where the and sign represent therelative currentcarrying sense of the coils and the figure 0 representsa coil omitted from circuit.

By contrast, by the present invention, the modulated connection of FIG.1(1)) is obtained solely by the re versal of selected coils andcoil-groups, according to the notation:

It will be noted that the end coil-groups of each modulation half-wavecomprise two coils connected in a first sense and one coil connected inopposite sense, to provide a resultant substantially equivalent to onecoil connected in the first sense, as in FIG. 1(a).

The current-carrying sense of the coils is chosen so that the coilsphysically placed next to the middle coil groups of each half-Wave areconnected in the same sense as those middle coil-groups, Whereas theouter coils of each half-wave are connected in opposite sense to allother coils of that half-wave.

In the slot-winding diagram of FIG. 2 and in the circuit diagrams ofFIGS. 3(a) and 3(1)), phase-winding A comprises symmetrical halves 21,22 serially connected between terminals 11, i2 and 17. Phase-winding Bcomprises the symmetrical halves 23, 24 serially connected betweenterminals 13, 14 and 17. Phasc-winding (3 comprises the symmetricalhalves 25, 26 serially connected between terminals 15, K and 17. In FIG.2, the same terminal i7 is shown at the ends of the three phase-windingswhich are connected together.

In FIG. 2, only phase-winding A is shown in full. Phase-windings B and Care both identical with phasewinding A but displaced from it by 24slots, one phasewinding in each direction. As shown in the figure, thephase-windings are wound to provide 8 poles with 3 slots per pole perphase, each coil being wound two-thirds of full pitch to 8 poles.

PIG. 3(a) shows the three phase-windings in parallelstar connectionproviding the lower, unmodulated, polenurnber of 8 poles. Terminals 11,13 and 15 are connected together. Terminals i2, 14 and 16 arerespectively connected by leads 31, 32 and 3?: to a 3-phase supply onlines L1, L2 and L3.

FIG. 3(b) shows the three phase-windings in seriesstar connectionproviding the modulated pole-nurnber of poles. Terminals 12, 1d and 16are isolated. Terminals ill, 13 and are respectively connected by theleads 31, 32 and 33 to the 3-phase supply on lines L L and L3.

it will be appreciated that the example described above has the lowerpole-number, that is S-poles, in the unnodulated connection and usesparallel-star/series-star alternative connections.

Often, as previously mentioned, it is preferred to reduce thepole-number by modulation and still to use the parallel-star connectionfor the lower po1e-number. Such an example of the invention would useseries-delta connection for the higher, unmodulated, pole-number andparallel-star connection for the lower, modulated, polenumber.

What I claim is:

1. A pole-changing rotary electric machine having a three-phase windingproviding a first pole-number of P pole-pairs and a second pole-numberselected from the pole-numbers (P+M) and (P-M) pole-pairs, where M isthe number of cycles of a modulation wave around the windingcircumference, having three phase-windings sequentially arranged aroundan axis, the electrical phasesequence A, B, C and phase-band sequence +A-C +B -A +C -B defining a reference sense of rotation around said axis,said phase-bands comprising coils connected together in eachphase-winding to provide 2P poles, switch means for connecting selectedones of said coils in an alternative manner to modulate the relativeamplitudes of said 2P poles according to three pole-amplitude modulationwaves applied one to each phase-winding in spaced relationship, eachpole-amplitude modulation wave comprising M cycles of alternate positiveand negative parts following sequentially from an origin, said positiveand negative parts being identified by reversal of polarity of the polesof said negative part relative to the poles of said positive part, thespaced relationship of said pole-amplitude modulation waves being suchas to space the origins thereof at three points spaced apartsubstantially one-third of a revolution around said axis, the sequenceof said poleamplitude modulation waves at said three spaced points beingin the phase sequence A, B, C, in the said reference sense of rotation,when said second pole-number is (F-l-IVI) pole-pairs and being in thephase sequence A, C, B, when said second pole-number is (P/l)pole-pairs, wherein neither said first pole-number nor said secondpole-number is a number divisible by three, wherein the said three-phasewinding is an integral-slot winding and wherein the pole-amplitude ofthe pole at at least one end of each half of each phase-winding isreduced in the alternative, that is to say modulated, connection, saidpoleamplitude reduction being effected by reversal in currentcarryingsense of selected coils relatively to all the remaining coils of thecoil-groups providing said poles of reduced amplitude, whereby all coilsof all phase-bands are included in circuit for both the first and thealternative connections.

2. A rotary electric machine as claimed in claim 1, in which, in eachphase winding, said P pole-pairs of said first pole-number divided bythe 2M half-cycles of said pole-amplitude modulation wave provides anumber of poles in each half-cycle exceeding three poles and at leastone of the first and last poles of said number of poles is reduced inamplitude in the alternative, that is to say modulated, connection.

3. A rotary electric machine as claimed in claim 2, in which one of saidfirst and last poles of said number of poles is reduced to substantiallyzero amplitude.

4. A rotary electric machine as claimed in claim 1, in which the saidselected coils for reversal in current-carrying sense are selected insuch manner that said selected coils are coils wound adjacent othercoils of the said three-phase winding which are reversed incurrent-carry ing sense in said alternative, that is to say modulated,connection.

5. A rotary electric machine as claimed in claim 1, in which that one ofsaid first and alternative connections which provides the lowerpole-number is a parallel-star connection of the phase-windings.

6. A rotary electric machine as claimed in claim 5, in which the saidalternative, that is to say modulated, connection provides the lowerpole-number, in which the connection providing P pole-pairs in aseries-delta connection of the phase-windings and the alternativeconnection is a parallel-star connection thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,715,204 8/55Siskind 318-224 2,820,93 8 1/ 5 8 Davies 318-224 2,850,690 9/58Rawcliife 318-224 3,016,482 1/62 Anderson 3 l8-224 3,070,734 12/62Rawcliffe 318224 ORIS L. RADER, Primary Examiner.

1. A POLE-CHANGING ROTARY ELECTRIC MACHINE HAVING A THREE-PHASE WINDINGPROVIDING A FIRST POLE-NUMBER OF P POLE-PAIRS AND A SECOND POLE-NUMBERSELECTED FROM THE POLE-NUMBERS (P+M) POLE-PAIRS, WHERE M IS THE NU-MBEROF CYCLES OF A MODULATION WAVE AROUND THE WINDING CIRCUMFERENCE, HAVINGTHREE PHASE-WINDINGS SEQUENTIALLY ARRANGED AROUND AND AXIS, THEELECTRICAL PHASESEQUENCE A, B, C AND PHASE-BAND SEQUENCE +A -C +B -A +C-B DEFINING A REFERENCE SENSE OF ROTATION AROUND SAID AXIS, SAIDPHASE-BANDS COMPRISING COILS CONNECTED TOGETHER IN EACH PHASE-WINDING TOPROVIDE 2P POLES, SWITCH MEANS FOR CONNECTING SELECTED ONES OF SAIDCOILS IN AN ALTERNATIVE MANNER TO MODULATE THE RELATIVE AMPLITUDES OFSAID 2P POLES ACCORDING TO THREE POLE-AMPLITUDE MODULATION WAVES APPLIEDONE TO EACH PHASE-WINDING IN SPACED RELATION, EACH POLE-AMPLITUDEMODULATION WAVE COMPRISING M CYCLES OF ALTERNATE POSITIVE AND NEGATIVEPORTS FOLLOWING SEQUENTIALLY FROM AN ORIGIN, SAID POSITIVE AND NEGATIVEPARTS BEIND IDENTIFIED BY REVERSAL OF POLARITY OF THE POLES OF SAIDNEGATIVE PART RELATIVE TO THE POLES OF SAID POSITIVE PART, THE SPACEDRELATIONSHIP OF SAID POLE-AMPLITUDE MODULATION WAVES BEING SUCH AS TOSPACE THE ORIGINS THEREOF AT THREE POINTS SPACED APART SUBSTANTIALLYONE-THIRD OF A REVOLUTION AROUND SAID AXIS, THE SEQUENCE OF SAIDPOLEAMPLITUDE MODULATION WAVES AT SAID THREE SPACED POINTS BEING IN THEPHASE SEQUENCE A, B, C, IN THE SAID REFERENCE SENSE OF ROTATION, WHENSAID SECOND POLE-NUMBER IS (P+M) POLE-PAIRS AND BEING IN THE PHASESEQUENCE A, C, B, WHEN SAID SECOND POLE-NUMBER IS (P-M) POLE-PAIRSWHEREIN NEITHER SAID FIRST POLE-NUMBER NOR SAID SECOND POLE-NUMBER IS ANUMBER DIVISIBLE BY THREE, WHEREIN THE SAID THREE-PHASE WINDING IS ANINTEGRAL-SLOT WINDING AND WHEREIN THE POLE-AMPLITUDE OF THE POLE AT ATLEAST ONE END OF EACH HALF OF EACH PHASE-WINDING IS REDUCED IN THEALTERNATIVE, THAT IS TO SAY MODULATED, CONNECTION, SAID POLEAMPLITUDEREDUCTION BEING EFFECTED BY REVERSAL IN CURRENTCARRYING SENSE OFSELECTED COILS RELATIVELY TO ALL THE REMAINING COILS OF THE COIL-GROUPSPROVIDING SAID POLES OF REDUCED AMPLITUDE, WHEREBY ALL COILS OF ALLPHASE-BANDS ARE INCLINED IN CIRCUIT FOR BOTY THE FIRST AND THEALTERNATIVE CONNECTIONS.